Mean link versus average plaquette tadpoles in lattice NRQCD

We compare mean-link and average plaquette tadpole renormalization schemes in the context of the quarkonium hyperfine splittings in lattice NRQCD. Sim ulations are done for the three quarkonium systems <c(c)over bar>, <b(c)ove r bar>, and <b(b)over bar>. The hyperfine splittings are computed both at l eading and at next-to-leading order in the relativistic expansion. Results are obtained at a large number of lattice spacings. A number of features em erge, all of which favor tadpole renormalization using mean links. This inc ludes much better scaling of the hyperfine splittings in the three quarkoni um systems. We also find that relativistic corrections to the spin splittin gs are smaller with mean-link tadpoles, particularly for the <c(c)over bar> and <b(c)over bar> systems. We also see signs of a breakdown in the NRQCD expansion when the bare quark mass falls below about one in lattice units ( with the bare quark masses turning out to be much larger with mean-link tad poles).